Bending of thermoplastic tubes

ABSTRACT

A method and apparatus for bending thermoplastic tube in which a pre-heated region of the tube is conformed to a required bend configuration while supported internally and externally to prevent the tube wall collapsing. The external support is provided by relatively movable formers which enclose a section of the tube at the point where the bending force is applied and this enclosed section moves progressively along the heated region as the bend is developed by the relative movement of the formers. The internal support is provided by fluid pressure higher than atmospheric pressure within the tube during the forming operation. Multiple bends can be formed sequentially and/or siitultateously.

This invention concerns improvements in or relating to bending ofthermoplastic tubes. More specifically, the invention provides animproved method or apparatus for bending of thermoplastic tubes. Theinvention has particular application t bending of thin wall large borethermoplastic tubes. As used herein, the term “tube” includes hoses,pipes or similar conduits, whether of single or multi-layerconstruction.

Thermoplastic tubes are used for many applications, for example in theautomotive field where the tube may have to be of a specificconfiguration with one or more bends to provide the necessary fluid flowconnection.

It is desirable to form such tubes having smooth bends with minimumdistortion of the tube wall giving non-turbulent flow to maintain theoptimum flow characteristics through the tube and produce anaesthetically pleasing appearance.

A method and apparatus for shaping thermoplastic tube is described in UKPatent No. 2249750-B in which the tube is pre-formed to a required bendconfiguration prior to effecting contactless heating of the bend regionby pulsed emission of infra-red radiation to soften the thermoplasticmaterial followed by air cooling to set the thermoplastic material andretain the required bend configuration.

The tube is pre-shaped on a jig with appropriately positioned sources ofinfra-red radiation and air to carry out the heating and cooling stageswith the tube held stationary on the jig.

With this method and apparatus, it is possible to produce tubes ofcomplex shape with multiple bends in different planes being formedsimultaneously. This method is particularly suitable for shaping smallbore thermoplastic tubes without requiring any internal support such asa separate removable mandrel to prevent the tube wall collapsing.

Problems can arise however in trying to shape thin wall large borethermoplastic tube by such method and apparatus. In particular, there isa much greater tendency for thin wall large bore tube to flatten acrosstheir section at 90° to the bend axis resulting in an elliptical shapedbore or, in extreme cases, the tube may fold or even collapse on ititself producing an unacceptably deformed tube.

As a result, it is still common for thin wall large bore tubes to beprovided with an internal solid mandrel which is flexible to allow thetube to be formed to the required shape and which is removed after thetube is set in the required shape. The use of such mandrels adds toproduction costs and restricts the shapes that can be produced withoutcompletely stopping the tube creasing. Thus, sufficient clearance has tobe allowed for insertion and removal of the mandrel. As a result, somecollapse of the tube wall may occur during forming and the formed lubemay be deformed by removal of the mandrel. In addition, lubricants whichare possible undesirable contaminants may have to be used to assistremoval of the mandrel.

It is an object of the present invention to provide an improved methodand apparatus for shaping thermoplastic tubes which enables bends to beformed in a wider range of tube sizes than previously.

It is a particular desired object of the present invention to provide animproved method and apparatus for shaping thin wall large borethermoplastic tubes.

It is a further preferred object of the present invention to provide animproved method and apparatus for shaping thin wall large borethermoplastic tubes which enables bends to be formed withoutsignificantly changing the bore section.

It is yet another preferred object of the present invention to providean improved method and apparatus for shaping thin wall large borethermoplastic tubes which enables bends to be formed having a smallradius or angle.

It is still further preferred object of the present invention to providean improved method and apparatus for shaping thin wall large borethermoplastic tubes to provide multiple bends in different planesenabling complex shapes to be produced.

According to one aspect of the present invention there is provided amethod of forming a bend having a required configuration in a tube ofthermoplastic material comprising locally heating a region of the tubein which a bend is to be formed until the plastic material becomessufficiently plastic for subsequent shaping to a required bendconfiguration, positioning the tube between relatively movable formersproviding external support around a section of the heated region of thetube, relatively moving the formers to form progressively the requiredbend configuration while simultaneously providing internal support forthe tube by a pressure differential between the inside and outside ofthe tube, and cooling the tube to set thermoplastic material and retainthe required bend configuration.

By this invented method, the formation of the bend with the requiredconfiguration is achieved without deforming or collapsing so as tomaintain substantially the original cross-section of the tube. This ismade possible in the invented method by supporting the tube internallyand externally during the bending operation.

In particular, the relatively movable formers enclose a section of thetube at the point where the bending force is applied and this enclosedsection moves progressively along the heated region as the bend isdeveloped by the relative movement of the farmers.

Preferably, the pressure differential is created by the provision of afluid medium, conveniently compressed air, within the tube during theforming operation. The fluid medium may be confined within the tube byappropriate sealing means at each end of the tube. Alternatively, thefluid medium may be confined in an inflatable bladder inserted into thetube.

Advantageously, cooling is effected externally and/or internally, forexample by a fluid medium, such as a gas or liquid, caused to flow overthe exterior andor through the interior of the tube by any suitablemeans,such as fans, blowers, sprays etc.

Preferably, the pressure differential is maintained during the coolingstage to prevent the tube deforming or collapsing before thethermoplastic material has set. This may be achieved by the use ofcompressed air both in the forming and cooling stages.

Advantageously, external support on the inside of the bend is maintainedas the bend is developed. For example, the tube may be progressivelyformed around a former having a profile corresponding substantially tothe profile of the required bend.

Preferably, external support on the outside of the bend is provided atthe point where bending forces are applied and moves along the tube asthe bend is developed. For example, a former for the outside of the bendmay move around the former for the inside of the bend. In this way, asthe bend is developed, the section of the tube being formed is totallyenclosed.

The formers may be relatively movable to form the bend in one or moreplanes. More than one bend may be formed at spaced apart positions alongthe length of the tube to produce complex configurations. Multiple bendsmay be in the same or different planes.

It may be possible with the invented method to form two bendssimultaneously with further bends produced in pairs sequentially alongthe length of the tube as desired.

According to another aspect of the present invention there is providedapparatus for forming a bend in a tube of thermoplastic materialcomprising means for heating a pre-determined region of a tube to softenthe plastic material for subsequent shaping, means for shaping theheated region of the tube to form a bend having a requiredconfiguration, and means for cooling the tube to set the thermoplasticmaterial and retain the required bend configuration, the shaping meansincluding relatively movable former means for externally supporting asection of the heated region of the tube at the point of bending andmeans for internally supporting the tube during the being operation by apressure differential between the inside and outside of the tube.

The former means provide localised external support around the tube asthe bend is formed, with the pressure differential providing internalsupport to prevent the tube collapsing or deforming.

Preferably, the former means comprises a fixed former having a profilecorresponding to the inside of the bend and a former movable around thefixed former to conform the tube to the profile of the fixed former andprovide support for the outside of the bend at the point of bending.

In this way, the section of the tube where the bending forces areapplied is totally enclosed by the formers and this external supportaround the tube is maintained locally by relative movement of theformers as the bend is developed.

Advantageously, the fixed former has a peripheral groove correspondingto the radius of the required bend around which the tube is formed andthe movable former has a peripheral groove co-operable with the groovein the fixed former to provide external support around the section ofthe tube therebetween. The peripheral groove in the fixed former may beof constant or variable radius and/or may be in one or more planesdepending on the desired shape and configuration of the finished bend.

Preferably, the groove in the fixed former is of U-shape in radialcross-section and is a depth sufficient to receive the tube and themarginal edge of the movable former. In this way the movable former isguided for movement around the fixed former to conform the tube to therequired configuration. Where the peripheral groove in the fixed formeris of variable radius and/or in more than one plane, the movable rollermay be adjustable to compensate for such changes so as to follow theprofile of the fixed former. For example, the movable former may bespring loaded and/or angularly adjustable.

Advantageously, means is provided for securing the tube in the formingmeans during the forming operation. For example, the tube may be clampedat a position adjacent to the end of the heated region where the bendingoperation begins leaving the other end of the tube free for conformingthe heated region to the required bend configuration.

Preferably, the means for internally supporting the tube comprises asource of fluid, e.g. compressed air, connectable to the interior of thetube via a valve in one of two seal units for the opposite endsrespectively of the tube. Alternatively, the fluid source is connectableto an inflatable bladder positioned within the tube.

Advantageously, the means for cooling the tube comprises a source offluid, e.g. a gas or liquid, passed over and/or through the tube. Wherecompressed air is used to provide internal support for the tube duringthe forming stage, the compressed air may be passed through the tube tocool the tube and maintain the internal support during the coolingstage.

The invention will now be described in more detail by way of exampleonly with reference to the accompanying drawings wherein:

FIG. 1 is a side view of a hearing unit of apparatus embodying theinvention;

FIG. 2 is an end view, to an enlarged scale and partly in section, ofthe heating unit shown in FIG. 1.

FIG. 3 is a side view of one half of the beating unit shown in FIG. 1;

FIG. 4 is an end view the half of the heating unit shown in FIG. 3;

FIG. 5 is an end view of a forming unit of apparatus embodying theinvention, with the moveable forming roller in the open position;

FIG. 6 is au end view, to an enlarged scale and partly in section, ofpart of the forming unit of FIG. 5 showing the forming roller in theclosed position;

FIG. 7 is a side view of the forming unit of FIG. 5 with the formingroller in the open position.

FIG. 8 is an end view showing the tube positioned in the fixed former ofFIG. 5;

FIG. 9 is a side view, similar to FIG. 7 showing the forming roller inthe closed position at the start of the bending cycle.

FIG. 10 is a side view, similar to FIG. 9, showing the forming roller inthe closed position at the end of the bending cycle;

FIG. 11 is a side view similar to FIG. 7, of a modified forming unit forproducing a bend of variable radius;

FIG. 12 is a side view of an alternative forming unit for producing asweeping bend;

FIG. 13 is a side view, similar to FIG. 12, of a modified forming unitfor producing a sweeping bend;

FIG. 14 is a side view of the forming unit shown in FIG. 13 showing theformation of the bend;

FIG. 15 is an end view, similar to FIG. 6, of a modified forming unitfor producing a bend in two planes;

FIG. 16 depicts schematically the stages of the method for shapingthermoplastic tube according to the invention;

FIG. 17 is a schematic side view of apparatus for forming multiplebends;

FIG. 18 is a schematic plan view of the apparatus shown in FIG. 17;

FIG. 19 is a schematic side view of the apparatus similar to FIG. 17showing a length of tube located at the start of the bending operation;

FIG. 20 is a plan view of a tube having multiple bends formed by theapparatus shown in FIGS. 17 to 19; and

FIG. 21 is a side view of the tube shown in FIG. 20.

Referring first to FIGS. 1 to 16 of the drawings, the method of forminga bend having a required configuration according to the invention willbe described briefly with reference to FIG. 16 followed by a descriptionof apparatus for carrying out the method with reference to FIGS. 1 to15.

As shown in FIG. 16, a length of thermoplastic tube of circular crosssection is first heated locally in the region 2 in which a bend is to beformed until the thermoplastic material softens sufficiently to allowsubsequent shaping.

During this heating stage, the interior of the tube 1 is open toatmosphere so that the pressure inside and outside the tube is the sameand heating is controlled to prevent the tube 1 from collapsing.

On completion of the heating stage, the tube is formed to the requiredbead configuration by progressively bending the heated region 2 of thetube 1 around a former 3 with a forming roller 4 while axially securingthe tube 1 as indicated by the arrow X adjacent to the end of the heatedregion 2 where the bending operation begins.

During this bending stage, the interior of the tube 1 is connected to asource of compressed air 50 that the pressure inside the tube 1 ishigher than atmospheric pressure outside the tube and the pressuredifferential is controlled to provide internal support for the tube 1during the bending operation. Alternatively, the internal support may beprovided by connecting the source of compressed air to an inflatablebladder (not shown) positioned in the tube 1 after the heating stage.The bladder may be partially inflated to assist insertion into the tubeprior to inflating fully to support the tube. The use of a bladder mayallow end fittings to be attached to the straight tube prior to shaping.

At the same time, external support for the tube 1 is provided by theformer 3 and former roller 4 which cooperate to enclose the tube 1 atthe point where pressure is applied during the bending operation. Thiscombination of internal and external support during the bending stageensures that the circular cross-section of the tube is maintainedthroughout the bend.

On completion of the bending stage, the tube 1 is externally cooled toset the thermoplastic material in the required bend configuration bypassing air over the outside of the tube 1. Alternatively or on inaddition, the tube 1 may be cooled internally by passing air through theinside of the tube 1.

During this cooling stage, the tube 1 is held in the required bendconfiguration until the thermoplastic material has set to retain thebend configuration. Where internal support is provided by an inflatablebladder, the bladder is preferably at least partially deflated after thethermoplastic material has set to facilitate removal.

The above-described method has application to thermoplastic tubes ofdifferent sizes but is especially suitable for forming bends in thinwall large bore tubes. The particular problems arising when shaping thinwall large bore tubes are avoided by the above method in which the tubeis pre-heated prior to shaping and fully supported internally andexternally during shaping. These and other advantages of the inventedmethod will be apparent for the following description of one apparatusfor carrying out the method.

Referring first to FIGS. 1 to 4, a heating unit 5 is shown for locallyheating the tube 1 in the region 2 in which the bend is to be formed.

The heating unit 5 comprises a rectangular block 6 split into two parts6 a, 6 b. Each part 6 a, 6 b is made of aluminium with a semicircularchannel 7 of slightly larger radius than the tube 1 in its inner surfaceand has a flat plate electrical heater 8 fixed to its outer surfacecovered by a sheet of thermal insulation material 9. Aluminium is thepreferred material for the block 6 because of its light weight andthermal conductivity properties but it will be understood that othermaterials could be used for the block 6.

The channels 7 co-operate in the closed condition of the block 6 shownin FIGS. 1 and 2 to surround the tube 1 with a small annular clearancespace 10 between the tube 1 and the block 6 so as to avoid directcontact between the tube 1 and the block 6 in the region 2 to be heated.

The upper part 6 a of the block 6 is movable relative to the lower part6 b in the direction indicated by the arrow A in FIG. 1 for loading andunloading of the tube 1. The tube 1 is supported at regions spaced fromeach end of the block 6 by insulated supports 11, 12 giving the annularclearance space 10 when the block 6 is closed.

The region 2 of the tube to be heated is determined by the position andlength of the bend to be formed and the length Y of the channel 7 isvaried accordingly. For example, the length Y of the channel 7 may bevaried by selecting the appropriate block 6 from sets of blocks 6 ofdifferent length. Alternatively, the length Y of the channel 7 may bevaried by arranging two or more blocks 6 of the same or different lengthin series.

The tube 1 is heated to soften the thermoplastic material in the region2 for the subsequent bending operation as previously described. Thetemperature is controlled by any suitable thermostatic device (notshown) to prevent the tube 1 melting or deforming in the region 2 whilethe clearance space 10 avoids contact with the block 6 to prevent damageto the surface of the tube 1 in the region 2.

Whilst located in the block 6, the interior of the tube 1 is open toatmosphere so that the pressure inside and outside the tube 1 is thesame. As a result, air is not trapped within the tube 1 and can escapefrom each end when the tube 1 is heated causing the air to expand. Inthis way, an uncontrollable increase in pressure within the tube 1 whichcould result in deformation of the tube 1 in the region 2 as thethermoplastic material softens is avoided.

Furthermore, energy is not expended in first heating and later coolingair trapped in the tube and there is less risk of heat transfer to theregions of the tube 1 outside the heating zone within the block 6. As aresult, the heating stage is more efficient and can be controlled moreeasily to ensure the tube 1 is heated to the required temperature.

Referring now to FIGS. 5 and 6, a forming unit 13 for shaping the tube 1to the required bend configuration is shown including former 3 andforming roller 4.

The former 3 is fixed and has a part annular peripheral groove 14 ofU-shape in radial cross-section. The groove 14 is of constant radiuscorresponding to the radius of the bend to be formed and is ofsufficient depth to receive the tube 1 as shown in FIG. 5.

The roller 4 is supported on a plate 15 for radial movement relative tothe former 3 under the control of a piston/cylinder device 16 between anopen position shown in FIG. 5 and a closed position shown in FIG. 6.

The roller 4 has an annular peripheral groove 17 of C-shape in radialcross-section co-operable with the groove 14 of the former 3 to enclosea section of the tube 1 in the closed position as shown in FIG. 6 inwhich the peripheral edge of the roller 4 is received between the sidewalls of the groove 14.

The plate 15 is rotatable by any suitable means (not shown) about anaxis 18 through the centre of curvature of the groove 14 for moving theroller 4 around the former 3 to form a bend having the requiredconfiguration.

The roller 4 is free to rotate about an axis 19 parallel to and spacedfrom the axis 18 for rolling engagement with the tube 1 as it movesaround the former 3 and the pressure applied by the roller 4 isadjustable through the piston/cylinder device 16 controlling radialmovement of the roller 4.

In this ways the cross-sectional shape of the tube 1 is maintained anddamage to the surface of the tube 1 substantially avoided during thebending operation. In particular, the former 3 and roller 4 totallyenclose the tube 1 at the point where pressure is applied to bend thetube 1 so that the bending forces are contained within the enclosedsection of the tube 1 and are resisted by the internal air pressure asthe bend is developed by the movement of the roller 4 around the former3 so that the tube 1 does not spread or flatten or fold or otherwisedeform or suffer surface damage during the bending operation.

Operation of the forming unit 13 will now be described with reference toFIGS. 7 to 10. Tube 1 from the heating unit 5 is loaded in the formingunit 13 with roller 4 in the open position by locating one end of thepreheated region 2 in the groove 14 of the former 3 opposite the roller4 as shown in FIGS. 7 and 8.

The tube 1 is secured in this position by closing a clamp device 20around an unheated region of the tube 1 adjacent to the end of theheated region 2 as shown in FIG. 9.

Seal units 21, 22 are fixed to opposite ends of the tube respectivelyand pressurised air introduced into the interior of the tube 1 through avalve (not shown) in the seal unit 21. The pressure is controlled tosupport the tube 1 without deforming the heated region 2.

The roller 4 is then moved to the closed position shown in FIG. 9 toenclose a section of the tube 1 at the end of the heated region 2 andmoved around the former 3 so that the heated region 2 of the tube 1 isformed progressively to the required bend configuration as shown in FIG.10.

At the end of the forming stage, the tube 1 is held in the required bendconfiguration at the end of the heated region 2 by the clamping device20 and at the other end between the former 3 and roller 4. Compressedair is then directed over the outer surface of the tube 1 from nozzles23 to cool rapidly the heated region 2 of the tube 1 to set thethermoplastic material and retain the formed bend configuration.

Compressed air may also be passed through the interior of the tube 1 byopening a valve in the other seal unit 22 to assist cooling whileretaining sufficient internal pressure to prevent the tube walldeforming. Cooling may be further assisted by the use of aluminium forthe former 3 to conduct heat away from the tube.

On completion of the cooling cycle, the roller 4 is returned to thestart position and the tube 1 released by moving the roller 4 to theopen position, releasing the clamp device 20 and removing the seal units21,22.

As will now be understood, the tube 1 is internally and externallysupported during the forming operation. The internal support is providedby creating a pressure differential between the interior and exterior ofthe tube 1 through the introduction of compressed air into the tube 1.The external support is provided on the inside of the bend by the former3 and on the outside of the bend by the roller 4 as it moves around theformer 3. The area where the former 3 initially contacts the tube 1 andwhere the roller 4 waits whilst cooling takes place are preferablyunheated in order to avoid creating an impression of the roller 4 in thetube 1 at these points.

By this combination of internal and external support, smooth bends canbe formed in which the original cross-section of the tube 1 ismaintained so that, in use, flow through the tube 1 is not affected.This is of particular benefit for the formation of bends in thin walllarge bore tubes which are especially susceptible to deformation whenbends are formed by other methods in which the tube is pre-shaped priorto heating and/or is not fully supported internally and externallyduring shaping. Thus, the invented method and apparatus has particularapplication to tubes in which the ratio of the diameter to the wallthickness of the tube is ≧8:1, more preferably ≧10:1 and especially≧12:1.

The above-described embodiment is especially suited to the formation oftight bends of small radius in which the bend angle may be altered asdesired by appropriate control of the angular movement of the roller 4to conform the tube 1 around the former 3.

The bend is of constant fixed radius but this is not essential and FIG.11 shows a modification in which the peripheral groove in the former 3is of part elliptical shape for producing a bend of variable radius. Inthis embodiment, the change in radius as the roller 4 moves around thegroove is compensated for by change in length of the piston/cylinderdevice 16 so that the roller 4 applies a constant force at the pointwhere it co-operates with the fixed former 3.

In addition to tight bends, the invented method and apparatus are alsosuitable for the formation of sweeping bends of large radius. Thus, asshown in FIG. 12, the piston/cylinder device 16 traverses a slideway 24to effect linear movement of the roller 4 and simultaneously changes inlength to adjust the position of the roller 4 so that the roller 4follows the groove in the fixed former 3 and applies a constant force atthe point where it co-operates with the former 3.

FIGS. 13 and 14 show a modification to FIG. 12 in which the slideway 24is pivoted at one end 24 a to adjust the position of the roller 4 as thepiston/cylinder device 16 traverses the slideway so that the roller 4follows the groove in the fixed former 3 and applies a constant force atthe point where it co-operates with the former 3. Pivotal movement ofthe slideway is controlled by a pusher unit 25 so that the axis of thepiston/cylinder device 16 is more normal to the face of the fixed former3 than is the case with the arrangement shown in FIG. 12.

The forming units above-described produce single bends in one plane andFIG. 15 shows a modification for producing a single bend in two planesby arranging that the roller 4 can slide in the direction of arrow Aparallel to its axis of rotation to follow a helical path provided bythe groove 14 in the fixed former 3. As shown, the roller 4 and former 3have angled flanks 26,27 to prevent the roller 4 jamming in the groove14. Alternatively, or in addition, the roller 4 may be spring loadedand/or angularly adjustable so as to follow the groove 14 and preventjamming. The groove 14 in the former 3 may be helical or any othersuitable shape.

Although the invention has been described thus far for the formation ofa single bend, it will be understood that the invented method andapparatus may be adapted to produce multiple bends in the same ordifferent planes allowing tubes of complex configuration to be producedfor any desired use.

FIGS. 17 to 19 show schematically the forming station 100 of anapparatus for producing the tube 101 shown in FIGS. 20 and 21.

As shown, the tube 101 is of complex shape having four bends 102, 103,104, 105 of different radius lying in different planes.

The forming station 100 comprises a separate former unit 106, 107, 108,109 for each bend.

Each former unit comprises a former 106 a, 107 a, 108 a, 109 a which isfixed during the forming operation and a former 106 b, 107 b, 108 b, 109b which is movable relative to the fixed former for conforming the tube101 to the required bend configuration as described previously.

Each former unit 106, 107, 108, 109 may be movable independently or incombination with another former unit for adjusting the relative spatialarrangement of the former pairs. Such movement may be effected oninitial set-up of the apparatus and/or between bending operationsdepending on the required configuration of the finished tube 101.

In this embodiment, each fixed former 106 a, 107 a, 108 a, 109 a has aperipheral groove 110 of constant radius and the associated movableformer 106 b, 107 b, 108 b, 109 b comprises a roller 111 having aperipheral groove 112 for co-operating with the groove 110 as describedpreviously,

Each roller 111 is mounted for rotation at one end of an arm 112. Theother end of the arm 112 is pivotally mounted at the centre of curvatureof the groove 110 of the associated fixed former 106 a, 107 a, 108 a,109 a.

Each arm 112 is length adjustable for moving the roller 111 in a radialdirection towards and away from the associated fixed former 106 a, 107a, 108 a, 109 a as shown by the arrows C between an open position forpositioning the tube 101 between each pair before forming and removingthe tube 101 after forming, and a closed position for the formingoperation.

Each arm 112 is also pivoted for moving the roller 111 around the fixedformer 106 a, 107 a, 103 a, 109 a as shown by the arrows D forconforming the tube 101 to the required bend configuration during theforming operation.

The grooves 110, 112 of each former pair 106, 107, 108, 109 areco-operable to enclose a section of the tube 101 therebetween in theclosed position as described previously. In this way, as the roller 111moves around the fixed former 106 a, 107 a, 108 a, 109 a, the tube 101is totally enclosed at the point where pressure is applied to conformthe tube 101 to the required bend configuration as described previously.

Operation of the apparatus to form the tube 101 shown in FIGS. 20 and 21will now be described.

Firstly, an appropriate length of the tube 101 of suitable thermoplasticmaterial is heated to soften the thermoplastic material sufficiently forconforming to the required bend configuration. This heating is effectedwith the tube 101 in a straight condition by a heating unit (not shown)similar to that described previously for heating either discretesections of the tube 101 where each bend is to be formed or the sectioncontaining all the bends leaving each end of the tube 101 unheated.

A heating station (not shown) may be provided comprising a plurality ofheating units arranged to heat the tubes 101 to the required conditionand deliver the heated tubes 101 in sequence to a loading station (notshown) according to a predetermined cycle for transfer to the formingstation 100.

At the loading station, a pair of seal units 113, 114 are attached toopposite ends of the tube 101 and compressed air admitted through asupply line 115 connected to one of the seal units to provide a pressureinside the tube 101 which is higher than atmospheric pressure outsidethe tube 101 for supporting the tube 101 internally during the bendingoperation.

The tube 101 with the seal units 113, 114 attached is transferred to theforming station 100 where it is positioned between the fixed formers 107a, 108 a and the associated rollers 111 of the inner pair of formerunits 107, 108 as shown in FIG. 19.

The rollers 111 are then moved from the open position to the closedposition locating the tube 101 at two spaced apart positions. The sealunits 113, 114 are then released from the transfer device (not shown) sothat both ends of the tube 101 are free for the subsequent bendingoperation. During this operation, the tube 101 may also be supported onthe underside by a platform 115 which can be raised and lowered in thedirection of arrow E to assist alignment of the tube 101 with the formerunits 107, 108.

With the tube 101 held by the inner pair of former units 107, 108, therollers 111 are moved relative to the associated fixed formers 107 a,108 a to form the bends 103, 104 simultaneously.

One end of the tube 101 extends vertically and is held temporarily by aclamp 116 while the former unit 106 is moved to the required positionfor forming the bend 102. The other end of the tube 101 extendshorizontally and is positioned relative to the former unit 109 forforming the bend 105.

The rollers 111 of each former unit 106, 109 are then moved towards theassociated fixed former 106 a, 109 a so that the tube 101 is heldbetween the outer pair of former units 106, 109.

The rollers 111 are then moved relative to the associated fixed formers106 a, 109 a to form the bends 102, 105 simultaneously.

With the tube 101 held in the required configuration, it is cooled byblowing compressed air over the outside and/or by passing compressed airthrough the inside. For this the seal unit at the other end remote fromthe supply of compressed air may be opened to allow the compressed airto escape while maintaining sufficient internal pressure to prevent thetube 101 collapsing. External cooling may be effected when all the bendshave been formed or when each bend is formed by providing a source ofcompressed air adjacent each bend region.

Once the tube 101 is cooled sufficiently to set the thermoplasticmaterial to retain the desired shape, the tube 101 is removed from theforming station 100 and seal units 113, 114 detached. The former units106, 107, 108, 109 are returned to the original position to receive tubenext tube 101 from the loading station via the transfer device.

As will be appreciated the apparatus above-described enables complexshapes with multiple bends to be produced while the cross-section of thetube 101 is maintained by the pressure differential created by thecompressed air admitted to the tube 101 to internally pressurise thetube 101 prior to forming the bends 102, 103, 104, 105. By forming thebends simultaneously and sequentially in pairs, the tube is held in arequired position without additional clamping. It will be understoodthat each bend could be formed in sequence although forming pairs ofbends simultaneously reduces cycle times and handling.

It will also be understood that the invented method and apparatus hasapplication to a wide range of thermoplastics materials includingpolyamide, polyurethane, polyethylene, polypropylene, polyvinylchloride,polyacetal, polybutyleneterephalate and other elastomers and copolymersof these thermoplastics.

It will be further understood that the invented method and apparatus maybe used to shape both mono-layer and multi-layer tubes. Multi-layertubes may comprise a single thermoplastics material or combinations oftwo or more different thermoplastics materials. For example, a tube wallcomprising layers of different thermoplastics material may be obtainedby co-extrusion of the thermoplastics material.

It will also be understood that the invented method and apparatus mayhave application to tubes with or without any reinforcement. Forexample, a reinforcement layer such as a metallic or non-metallic sleevemay be incorporated in the tube wall during manufacture. Alternatively,reinforcement material, such as glass or carbon fibre may beincorporated into the thermoplastics material forming the tube wall.

Finally, it will be understood that tubes may be formed by the inventedmethod and apparatus for a wide range of diverse applications which mayrequire specific grades of thermoplastics Materials to be used with orwithout reinforcement as mentioned above and/or end fittings at one orboth ends to connect the tube for its intended use. For example, fuelfiller pipes fuel vapour pipes, ventilation pipes, drain pipes andcoolant pipes may be formed by the invented method and apparatus.

What is claimed is:
 1. A method of forming a bend having a requiredconfiguration in a tube of thermoplastic material comprising heating aregion of a tube in which a bend is to be formed while maintaining thepressure inside and outside of the tube at substantially atmosphericpressure, until said thermoplastic material becomes sufficiently plasticfor subsequent shaping to a required bend configuration, positioningsaid tube between relatively movable formers providing external supportaround a section of said heated region of said tube, relatively movingsaid formers to form progressively said required bend configurationwhile simultaneously providing internal support for said tube by apressure differential between the inside and outside of said tube, andcooling said tube to set said thermoplastic material and retain saidrequired bend configuration.
 2. A method according to claim 1 whereinsaid pressure differential is created by the provision of a fluid mediumwithin said tube during said forming operation.
 3. A method according toclaim 2 wherein said fluid medium is confined within said tube bysealing means at each end of said tube.
 4. A method according to claim 1wherein cooling is effected by a fluid medium caused to flow over theexterior and/or through the interior of said tube.
 5. A method accordingto claim 1 wherein said pressure differential is maintained during saidcooling stage.
 6. A method according to claim 1 wherein external supporton the inside of said bend is maintained as the bend is developed.
 7. Amethod according to claim 1 wherein external support on the outside ofsaid bend is provided locally at the point where bending forces areapplied and moves along said tube as said bend is developed.
 8. A methodaccording to claim 1 wherein said tube is totally enclosed between saidformers at the point where bending forces are applied.
 9. A methodaccording to claim 1 wherein a plurality of bends are formed at spacedapart positions along the length of said tube.
 10. A method according toclaim 9 wherein multiple bends are formed in the same or differentplanes.
 11. A method according to claim 9 wherein multiple bends areformed simultaneously.
 12. A method according to claim 9 whereinmultiple ends are formed sequentially.
 13. Apparatus for forming a bendin a tube of thermoplastic material comprising means for heating apre-determined region of a tube while maintaining the pressure insideand outside of the tube at substantially atmospheric pressure to softensaid thermoplastic material for subsequent shaping, means for shapingsaid heated region of said tube to form a bend having a requiredconfiguration, and means for cooling said tube to set said thermoplasticmaterial and retain the required bend configuration, said shaping meansincluding relatively movable former means for externally supporting asection of said heated region of said tube at the point of bending andmeans for internally supporting said tube during said bending operationby a pressure differential between the inside and outside of said tube.14. Apparatus according to claim 13 wherein said former means providelocalised external support around said tube as said bend is formed. 15.Apparatus according to claim 13 wherein said former means comprises afixed former having a profile corresponding to the inside of said bendand a former movable around said fixed former to conform said tube tosaid profile of said fixed former and provide support for the outside ofsaid bend at the point of bending.
 16. Apparatus according to claim 15wherein said fixed former has a peripheral groove corresponding to theradius of said required bend around which said tube is formed and saidmovable former has a peripheral groove co-operable with said groove insaid fixed former to provide external support around the section of saidtube therebetween.
 17. Apparatus according to claim 16 wherein saidgroove in said fixed former is of U-shape in radial cross-section and isa depth sufficient to receive said tube and the marginal edge of saidmovable former.
 18. Apparatus according to claim 15 wherein said formermeans comprises a plurality of former units each comprising a fixedformer and a movable former arranged at a forming station for producinga plurality of bends.
 19. Apparatus according to claim 13 wherein saidmeans for internally supporting said tube comprises a source of fluidconnectable to the interior of said tube.
 20. Apparatus according toclaim 13 wherein said means for cooling said tube is arranged to coolthe interior and/or exterior of said tube.
 21. The method according toclaim 1 further comprising ceasing heating of said tube prior topositioning of said tube.
 22. The method according to claim 1 furthercomprising: enclosing a section of said heated region of said tubebetween relatively movable formers providing external support aroundsaid enclosed section of said heated region of said tube, relativelymoving said formers to enclose discrete sections of said heated regionof said tube in turn and apply a bending force to each said enclosedsection to form progressively said required bend configuration whilesimultaneously providing internal support for said tube by a pressuredifferential between the inside and outside of said tube.
 23. Theapparatus according to claim 13 further comprising means for ceasingheating of said tube prior to shaping of said tube.
 24. The apparatusaccording to claim 13 wherein said shaping means further comprisesrelatively movable former means for enclosing and externally supportingdiscrete sections of said heated region of said tube in turn and apply abending force to each enclosed section to form progressively said bend.25. A method of forming a bend having a required configuration in a tubeof thermoplastic material comprising: heating a region of a tube inwhich a bend is to be formed until said thermoplastic material becomessufficiently plastic for subsequent shaping to a required bendconfiguration; enclosing a section of said heated region of said tubebetween relatively movable formers providing external support aroundsaid enclosed section of said heated region of said tube; relativelymoving said formers to enclose discrete sections of said heated regionof said tube in turn and apply a bending force to each said enclosedsection to form progressively said required bend configuration whilesimultaneously providing internal support for said tube by a pressuredifferential between the inside and outside of said tube; and coolingsaid tube to set said thermoplastic material and retain said requiredbend configuration.
 26. Apparatus for forming a bend in a tube ofthermoplastic material comprising: means for heating a pre-determinedregion of a tube to soften said thermoplastic material for subsequentshaping; means for shaping said heated region of said tube to form abend having a required configuration, said shaping means includingrelatively movable former means for enclosing and externally supportingdiscrete sections of said heated region of said tube in turn and apply abending force to each enclosed section to form progressively the bend;means for cooling said tube to set said thermoplastic material andretain the required bend configuration; and means for internallysupporting said tube during said bending operation by a pressuredifferential between the inside and outside of said tube.